The invention relates to a roll stand comprising two rolls forming a roll gap, which can be driven by their separate driving motors via drive spindles, in particular to a four-high stand, wherein for each roll a separate drive train is used, each comprising a toothed coupling in combination with a further flexible coupling.
In a roll stand, the arrangement of two driving motors--a so-called twin drive--as a consequence of the large center-to-center distance of the motor drive shafts requires large angles of inclination of the drive spindles or, if these are to be avoided, drive spindles of corresponding length, which would, however, result in a torsionally flexible drive. This problem is encountered especially with four-high reversing stands, where the vertical adjustment travel of the upper work roll is considerable.
For arranging drive spindles having a larger angle of inclination it is known to provide cardan shafts comprising universal joints. Drive spindles having large angles of inclination are, however, associated with the disadvantage that at a predetermined diameter of the universal joints--which on account of the relatively small diameter of the work rolls cannot exceed a certain dimension--they can transmit only relatively small torques. The reason for this is that one is limited in the dimensioning of the cross pins of the universal joints; especially with greater angular positions, the cross pins call for great outside diameters of the universal joints.
From JP-A--60-37205 a roll stand is known in which each of the rolls is connected via a first toothed coupling with a first shaft and via a second toothed coupling with a connecting shaft and further via a universal joint with a flexible shaft and a further universal joint with a driving motor or a further flexible shaft. The connecting shafts are mounted in an adjustable guide and are arranged so as to be parallel with respect to each other. As a result, relatively large angles have to be absorbed by the toothed couplings, as a sufficiently great distance has to be created between the universal joints arranged on the connecting shafts. This considerably increases the wear of the toothed couplings. A further drawback of the known roll stand is to be seen in the fact that the distance between motor and roll stand is very great, resulting in a space-consuming drive arrangement. This also results in the transmission of momentum from the driving motors to the work rolls being too soft.
From JP-A--61-193711 a roll stand of the kind initially described is known which is of a design similar to the roll stand described in JP-A--60-37205. Each of the two rolls is via a toothed coupling connected with a first shaft and via a flexible coupling permitting greater angular deviations, such as a universal joint, with a flexible shaft and via a further such flexible coupling with a respective drive motor or gear. Thus each drive train is formed by two flexible shafts, which, as the flexible couplings for greater angular recesses require more space, results in a great distance between motor and roll stand, involving the disadvantage of the transmission of momentum from the drive motors to the work rolls being too soft. On account of the universal joints being disposed opposite to each other in accordance with the known roll stand, there result large angles of inclination of the flexible shafts with respect to each other, which have to be compensated for by the universal joints. This entrains increased signs of wear, so that the service life of the universal joints will not be very long. Further, the known construction involves extensive maintenance costs.